Tool holder

ABSTRACT

Device at tool holder ( 10 ) of the kind comprising an essentially C-shaped frame preferably having a long inner range, which frame at its free shank ends carries said tool, for instance a riveting, a glueing or a welding unit. The holder ( 10 ) comprises a truss or frame work, which includes an outer and an inner C-shaped frame ( 11, 23 ) and a number of slewing brackets ( 27–32 ) connected to these. The frames ( 11, 23 ) and the slewing brackets ( 27–32 ) are arranged to form a number of connected triangular sections, which connection points ( 18–22, 37 ) are designed as intersections or joints. The outer C-shaped frame ( 11 ) is arranged only to support thrust forces and the inner frame ( 23 ) thrust and tensile forces and the slewing brackets ( 27–32 ) substantially tensile forces.

This application is a continuation of Ser. No. 09/733,260 filed Dec. 8,2000, now U.S. Pat. No. 6,467,826, which is a continuation ofPCT/SE99/01106 filed Jun. 18, 1999 designating the United States, whichPCT application was published in English under PCT Article 21(2)(a).

The present invention relates to a device in tool holders and of thekind which comprises a C-shaped frame, has a preferably long innerrange, which frame at its free shank ends carries said tool, for examplea riveting, a glueing or a welding unit.

THE BACKGROUND OF THE INVENTION AND THE PROBLEM

C-shaped frames of the above mentioned kind are previously known and areused for joining of for instance car body components, frame works, traincars, air crafts, etc. They are made as I-shaped section in high tensilesteel since high requirements are put on the stiffness and thestructural strength of the frame. Particularly when working operations,such as e.g. riveting, is in question, large opening forces arise on theshanks of the C-shaped frame. The frame is also to be exposed to a largenumber of working cycles and a minimum of 2 millions cycles is a demand.The C-frame must be able to operate on deeply situated parts in certainsituations, i.e, be able to reach a working area which is situated e.g.1 meter inside an outer limitation. At large scale production in theautomotive industry the C-shaped tool holder is being handled by arobot, which means that the weight of the C-frame should be so low thatthe total weight of the system is less than the allowed operation weightof the robot. At manual operation it is also desired to minimize themass of the system.

Using the robots of today, one has reached and in some cases alsoexceeded the weight limit, but the market demands both larger and morestable tool holders with maintained or even lowered weight. Theinvestments in robots are so high that it must be possible to useexisting ones even for new and more extensive working operations.

Tests have been made to produce C-shaped frames from composite materialsas solid models but the load strains in the intersections in the form,i.a., of shear and tear stresses in the glue joints will become so high,that these tests could not be performed. A typical steel C-frame, havingan inner depth of 850 mm, a gap between the ends of the shanks of 400 mmand a calculated load in the form of opposed directed forces of 53 kN,has a weight of about 150 kg at a maximal permitted deflection of 7 mmbetween the ends of the shanks. This weight together with the weight ofthe necessary tool equipment exceed the carrying and operatingcapability of the robot and are therefore not acceptable.

THE OBJECT OF THE INVENTION AND THE SOLUTION OF THE PROBLEM

The object of the invention is to provide a tool holder, which:

-   -   a. has a low weight,    -   b. has a high stiffness,    -   c. has a high strength,    -   d. has a simple construction,    -   e. is price-worthy,    -   f. can easily be varied in shape and form,    -   g. can operate in difficult environments, e.g., welding        sputters,    -   h. has a long service life and high reliability.

These tasks have been solved by the features defined in the claims.

DESCRIPTION OF THE DRAWINGS

The invention will be closer described below as an embodiment withreference to the enclosed drawings.

FIG. 1 shows in perspective a tool holder according to the inventionwith one front covering plate removed.

FIGS. 2 and 3 show two of the intersections also in perspective, moreexactly the front, upper and lower intersection respectively and therear, upper and lower intersection respectively.

FIG. 4 shows a rear intersection in perspective.

FIG. 5 shows a triangular connecting element in perspective.

FIG. 6 shows a side view of a modified tool holder according to theinvention.

FIG. 7 shows a frame element for the tool holder shown in side view inFIG. 6.

FIG. 8 shows the tool holder according to FIG. 1 in a loaded state.

FIG. 9 shows an unloaded tool holder according to a modified embodiment.

FIG. 10 shows the tool holder according to FIG. 9 in a loaded state.

DESCRIPTION OF AN EMBODIMENT

The tool holder according to the invention consists of an outer C-shapedframe 11, which in turn includes six frame beams 12–17, of which beams12, 13 and 17, 16 form the shanks of the C and the beams 14 and 15 theintermediate part between the shanks. Beams 12–17 are interconnectedend-to-end via intersections 18–22, so that they together form a C.

Inside the outer C-shaped frame 11, is provided a second C-shaped innerframe 23, comprising the frame beams 24 and 25, which also form theshanks of the inner frame 23, while its intermediate part between theshanks consists of beam part 26.

The outer and the inner C-frame 11,23 are interconnected partly viaslewing brackets 27 to 32 and at the end of the shanks via unitattachments 33 and 34. The intersections 18–22 are designed withconnecting ears 35 having a through bore 36 for shaft journal, whichform articulated joints 37 for the slewing brackets 27–32. In the sameway the inner connections between the slewing brackets and the innerframe 23 are designed as joints 37. The beam part 26 and the slewingbrackets 29, 30 are designed as a fixed triangular construction part 38,at which is provided a holder attachment 39 e.g. for a robot arm (notshown).

The intersections 18–22 and the unit attachments 33,34 are designed withguide flanges 40 and thrust areas 41 for guidance of and pressuretransfer to the end part and end areas 42 respectively of frame beams12–17. By angularly adjustment the thrust areas 41 of the intersections,the ends of the frame beams can be cut perpendicularly, which simplifiesmanufacturing.

The torsional rigidity in the C-shaped frame is suitably obtained by theattachment of stiffening plates 43 at both its flat sides, whichsuitably are connected to the frame beams 12–17 and 24, 25 during loadsubjected to the frame. The connection can be a glue joint, rivetedjoint or screw joint or the like. The material can be steel, aluminium,fibre reinforced plastic plates or equal.

In early construction work it proved itself that a frame workconstruction with intersections free from moments for weight reasons waspreferred above a construction having moment absorbing intersections.Solutions comprising moment supporting intersections must be maderelatively heavy and unwieldy to be able to handle the heavy loads. Thekey to achieving a light and durable construction showed to be designingthe geometry of the frame work thus that all incoming bars to anintersection meet at one common point. The selected geometry resulted inthat the C-frame 11 is put together by a number of interconnectedtriangles, where at least one side of a triangle is shared with theadjacent triangle.

Since the specific stiffness for composite materials exceeds the one forsteel, it is desirable to use as high a ratio of composite material aspossible to minimize the weight for the selected stiffness. The chosenconstruction principle with essentially moment-free intersection resultsin the outer frame being subjected to only one-axis loads; i.e.,compressing strains, whereby composite material is especially suitable.As composite material can be used different kinds of reinforced plastice.g., carbon fiber reinforced plastic, having a coefficient ofelasticity of about 95 in longitudinal direction compared to about 25for steel, which means that the carbon fiber frame is almost four timeslighter than the corresponding steel frame. Since also combined loadsarise in the inner parts of the outer frame and steel is a more costeffective construction material, these parts may suitably be of steel ora combination of steel and carbon fiber reinforced plastic, which in thedescribed embodiment has been selected for the frame beams 24 and 25,where the inner part of the frame beam is a carbon fiber beam 44 and theouter parts are steel rods. The weight of the whole tool holder is abouthalf the weight of a steel frame having corresponding performance.

However, this does not exclude, that selected parts of the constructioncan be replaced of composite material, in case the requirements oflowering the weight and/or stiffness and strength are further increasedeven more.

In order to optimize the properties of the material the fibres areoriented in the extension of the beams, i.e., longitudinally, whichmeans that the beams can be sawed from carbon reinforced plastic platesand be cut into suitable lengths, whereby the costs for the mostexpensive parts in the construction can be kept low. The selectedconstruction principle does not require special moulding tools, butpermits shell-moulding and modification without large initial costs.

The modified embodiment shown in FIGS. 6 and 7 differs from the abovedescribed in that several joints have been replaced by fixedintersections, but with the maintained requirement, that all connectionpoints are moment-free. By this design it is possible to fixedly connectthe slewing brackets 27, 28, 31 and 32 to the frame element 38, as toobtain the appearance shown in FIG. 7. The intersections 18–22 arefixedly integrated to the slewing brackets as to reduce the number ofassociated parts. The frame element 38 is suitably made of metal, forexample of steel. The inner frame beam is 24 and 25 are in the same wayas before articulately connected to the frame element 38.

A disadvantage of designing all intersection points free of moments, isthat the tool holder is so deformed during a load, see FIG. 8, that theconnection surfaces of the unit attachments 33, 34 not remain parallelbut will form an angle α with the horizontal plane.

When high requirements are put on the accuracy in the working process,i.e., that both parts of the tool unit 45, which can be a riveting unit45 a and a riveting knob 45 b, are essentially in alignment during theriveting operation, or in other words that the connection surfaces ofthe unit attachments 33, 34 essentially remain parallel, the principlewith the moment free intersections or joints can not be established. Tobe able to control the deformations of the C-shaped tool holder at load,it is suitable that moment is applied into one or more intersections orbars, which is achieved by that the centre line 46 of the incoming rodsto an intersection do not meet in a common intersection point. Thereforeall intersections will not be moment free.

In FIG. 9 it is shown how to control the deformation, to achieve certainrequirements, e.g., the above mentioned parallelism. In the unitattachment 33 the intersection point 47 of the centre line 46 has beenmoved outside the attachment 33, as to induce a moment using the momentarm 49 when for instance a riveting load, as shown by arrows 50, attacksthe unit attachments 33 and 34.

Further has moment been applied into the intersections 20 and 21, bydisplacing the attachment points 48, 51 of the frame beams 14, 15, 16corresponding to the length of the moment arms 52 and 53. Thereby theframe beam 16, 25 and 13, 24 are deformed axially and through bending.FIG. 10 gives an example of this, whereby the parallelism of theconnection surfaces of the unit attachments 33, 34 can be maintained.

Intersection point 101 is shown, at which the load line 50 intersectswith the center line 46 of said first outer shank portion 16 at anintersection point 101 located closer to a central portion of the toolholder, along the center line 46 of said first outer shank portion 16,than the intersection point 47 at which the center line 46 of the firstinner shank portion 25 and the center line 46 of the first outer shankportion 16 intersect.

In this embodiment the stiffening plates 43 are omitted.

The invention is not limited to the embodiment described and shown, buta number of variations are possible within the scope of the claims.Thus, the holder may consist of a larger or smaller number of triangularsections and different constructions of intersection joints arepossible.

LIST OF REFERENCE NUMERALS

-   10 tool holder-   11 outer C-frame-   12–17 outer frame beams-   18–22 intersections-   23 inner C-frame-   24,25 inner frame beams-   26 beam part-   27–32 slewing brackets-   33,34 unit attachments-   35 connecting ears-   36 boles-   37 joint/shaft journals-   38 frame element-   39 holder attachments-   40 guide flanges-   41 thrusts areas-   42 end areas-   43 stiffening plate-   44 carbon fibre beam-   45 tool unit-   46 a riveting unit-   45 b riveting knob-   46 centerline-   47 1^(st) intersectional point-   48 2^(nd) intersectional point-   49 moment arm-   50 force arrows-   51 3^(rd) intersectional point-   52,53 moment arm

1. A substantially C-shaped tool holder comprising: first and secondshank portions, each with a free shank end, and an interveningconstruction port ion, said shank portions and said construction portionlying substantially in a common plane, each free shank end having arespective connection surface facing the other free shank end, theconnection surfaces of the free shank ends, in the absence of a loadtherebetween, being in a first angular orientation relative to eachother, said tool holder further comprising: an inner C-shaped frame,having a first inner shank portion and a second inner shank portion andan inner construction portion therebetween; an outer C-shaped frame,having a first outer shank portion, a second outer shank portion; athird outer shank portion, and a fourth outer shank portion wherein thethird and fourth shank portions are located between the first and secondshank portions; wherein the frames are made from components each framehaving a defined center line, the tool holder further comprising: aplurality of brackets including a first bracket and a second bracket,each bracket having a respective first end and a respective second end,each bracket connecting the inner C-shaped frame to the outer C-shapedframe, thereby defining for each bracket a respective first point ofattachment between the first end of the bracket and the inner C-shapedframe and a respective second point of attachment between the second endof each bracket and the outer C-shaped frame, the first bracket having adefined center line, wherein the center lines of the first bracket, thefirst outer shank portion, and the third outer shank portion define amoment arm between: the center line of the first outer shank portion ofthe outer C-shaped frame; and an intersection of the center line of thefirst bracket and the center line of the third outer shank portion ofthe outer C-shaped frame; wherein the first inner shank portioninterconnects with the first outer shank portion at the first free shankend, and the second inner shank portion interconnects with the secondouter shank portion at the second free shank end, and wherein the centerlines of the components of the first inner shank portion and the firstouter shank portion, and a load line extending between the free shankends under load, do not all intersect at a single common intersectionpoint, and wherein the load line intersects with the center line of saidfirst outer shank portion at an intersection point located closer to acentral portion of the tool holder, along the center line of said firstouter shank portion, than the intersection point at which the centerline of the first inner shank portion and the center line of the firstouter shank portion intersect; whereby in the event of a load urging thefree shank ends apart, a moment is introduced by the load, forcing theconnection surfaces of the free shank ends apart only essentially alongthe extension of the load line, thereby preserving the first angularorientation.
 2. The tool holder of claim 1 further characterized inthat: the second bracket has a defined center line, wherein the centerlines of the second bracket, the third outer shank portion, and thefourth outer shank portion define a moment arm between: the center lineof the fourth outer shank port ion of the outer C-shaped frame; and anintersection of the center line of the second bracket and the centerline of the third outer shank portion of the outer C-shaped frame. 3.The tool holder of claim 1, wherein the construction portion of theinner C-shaped frame and and two brackets of the plurality of bracketsconnecting the construction portion of the inner C-shaped frame to theouter C-shaped frame are fabricated as a unitary triangular frameelement.
 4. The tool holder of claim 3, wherein the unitary triangularframe element has an attachment point for carrying the tool holder.
 5. Asubstantially C-shaped tool holder comprising: first and second shankportions, each with a free shank end, and an intervening constructionportion, said shank portions and said construction portion lyingsubstantially in a common plane, each free shank end having a respectiveconnection surface facing the other free shank end, the connectionsurfaces of the free shank ends, in the absence of a load therebetween,being in a first angular orientation relative to each other, said toolholder further comprising: an inner C-shaped frame, having a first innershank portion and a second inner shank portion and an inner constructionportion therebetween; an outer C-shaped frame, having a first outershank portion, a second outer shank portion; a third outer shankportion, and a fourth outer shank portion wherein the third and fourthshank portions are located between the first and second shank portions;wherein the frames are made from components each frame having a definedcenter line, the tool holder further comprising: a plurality of bracketsincluding a first bracket and a second bracket, each bracket having arespective first end and a respective second end, each bracketconnecting the inner C-shaped frame to the outer C-shaped frame, therebydefining for each bracket a respective first point of attachment betweenthe first end of the bracket and the inner C-shaped frame and arespective second point of attachment between the second end of eachbracket and the outer C-shaped frame, the second bracket having adefined center line, wherein the center lines of the second bracket, thethird outer shank portion, and the fourth outer shank portion define amoment arm between: the center line of the fourth outer shank portion ofthe outer C-shaped frame; and an intersection of the center line of thesecond bracket and the center line of the third outer shank portion ofthe outer C-shaped frame; wherein the first inner shank portioninterconnects with the first outer shank portion at the first free shankend, and the second inner shank portion interconnects with the secondouter shank portion at the second free shank end, and wherein the centerlines of the components of the first inner shank portion and the firstouter shank portion, and a load line extending between the free shankends under load, do not all intersect at a single common intersectionpoint, and wherein the load line intersects with the center line of saidfirst outer shank portion at an intersection point located closer to acentral portion of the tool holder, along the center line of said firstouter shank portion, than the intersection point at which the centerline of the first inner shank portion and the center line of the firstouter shank portion intersect; whereby in the event of a load urging thefree shank ends apart, a moment is introduced by the load, forcing theconnection surfaces of the free shank ends apart only essentially alongthe extension of the load line, thereby preserving the first angularorientation.
 6. The tool holder of claim 5 farther characterized inthat: the first bracket has a defined center line, wherein the centerlines of the first bracket, the first outer shank port ion, and thethird outer shank portion define a moment arm between: the center lineof the first outer shank portion of the outer C-shaped frame; and anintersection of the center line of the first bracket and the center lineof the third outer shank portion of the outer C-shaped frame.
 7. Thetool holder of claim 5, wherein the construction portion of the innerC-shaped frame and and two brackets of the plurality of bracketsconnecting the construction portion of the inner C-shaped frame to theouter C-shaped frame are fabricated as a unitary triangular frameelement.
 8. The tool holder of claim 7, wherein the unitary triangularframe element has an attachment point for carrying the tool holder.
 9. Asubstantially C-shaped tool holder comprising: first and second shankportions, each with a free shank end, a tool mechanically coupled witheach of the free shank ends, and an intervening construction portion,said shank portions and said construction portion lying substantially ina common plane, each free shank end having a respective connectionsurface facing the other free shank end, the connection surfaces of thefree shank ends, in the absence of a load therebetween, being in a firstangular orientation relative to each other, said tool holder furthercomprising: an inner C-shaped frame, having a first inner shank portionand a second inner shank portion and an inner construction portiontherebetween; an outer C-shaped frame, having a first outer shankportion, a second outer shank portion; a third outer shank portion, anda fourth outer shank portion wherein the third and fourth shank portionsare located between the first and second shank portions; wherein theframes are made from components each frame having a defined center line,the tool holder further comprising: a plurality of brackets including afirst bracket and a second bracket, each bracket having a respectivefirst end and a respective second end, each bracket connecting the innerC-shaped frame to the outer C-shaped frame, thereby defining for eachbracket a respective first point of attachment between the first end ofthe bracket and the inner C-shaped frame and a respective second pointof attachment between the second end of each bracket and the outerC-shaped frame, the first bracket having a defined center line, whereinthe center lines of the first bracket, the first outer shank portion,and the third outer shank portion define a moment arm between: thecenter line of the first outer shank portion of the outer C-shapedframe; and an intersection of the center line of the first bracket andthe center line of the third outer shank portion of the outer C-shapedframe; wherein the first inner shank portion interconnects with thefirst outer shank portion at the first free shank end, and the secondinner shank portion interconnects with the second outer shank portion atthe second free shank end, and wherein the center lines of thecomponents of the first inner shank portion and the first outer shankportion, and a load line extending between the free shank ends underload, do not all intersect at a single common intersection point, andwherein the load line intersects with the center line of said firstouter shank portion at an intersection point located closer to a centralportion of the tool holder, along the center line of said first outershank portion, than the intersection point at which the center line ofthe first inner shank portion and the center line of the first outershank portion intersect; whereby in the event of a load urging the freeshank ends apart, a moment is introduced by the load, forcing theconnection surfaces of the free shank ends apart only essentially alongthe extension of the load line, thereby preserving the first angularorientation.
 10. The combination of claim 9 further characterized inthat: the second bracket has a defined center line, wherein the centerlines of the second bracket, the third outer shank portion, and thefourth outer shank portion define a moment arm between: the center lineof the fourth outer shank portion of the outer C-shaped frame; and anintersection of the center line of the second bracket and the centerline of the third outer shank portion of the outer C-shaped frame. 11.The tool holder of claim 9, wherein the construction portion of theinner C-shaped frame and and two brackets of the plurality of bracketsconnecting the construction portion of the inner C-shaped frame to theouter C-shaped frame are fabricated as a unitary triangular frameelement.
 12. The tool holder of claim 11, wherein the unitary triangularframe element has an attachment point for carrying the tool holder. 13.A substantially C-shaped tool holder comprising: first and second shankportions, each with a free shank end, a tool mechanically coupled withthe free shank ends, and an intervening construction portion, said shankportions and said construction portion lying substantially in a commonplane, each free shank end having a respective connection surface facingthe other free shank end, the connection surfaces of the free shankends, in the absence of a load therebetween, being in a first angularorientation relative to each other, said tool holder further comprising:an inner C-shaped frame, having a first inner shank portion and a secondinner shank portion and an inner construction portion therebetween; anouter C-shaped frame, having a first outer shank portion, a second outershank portion; a third outer shank portion, and a fourth outer shankportion wherein the third and fourth shank portions are located betweenthe first and second shank portions; wherein the frames are made fromcomponents each frame having a defined center line, the tool holderfurther comprising: a plurality of brackets including a first bracketand a second bracket, each bracket having a respective first end and arespective second end, each bracket connecting the inner C-shaped frameto the outer C-shaped frame, thereby defining for each bracket arespective first point of attachment between the first end of thebracket and the inner C-shaped frame and a respective second point ofattachment between the second end of each bracket and the outer C-shapedframe, the second bracket having a defined center line, wherein thecenter lines of the second bracket, the third outer shank portion, andthe fourth outer shank portion define a moment arm between: the centerline of the fourth outer shank portion of the outer C-shaped frame; andan intersection of the center line of the second bracket and the centerline of the third outer shank portion of the outer C-shaped frame;wherein the first inner shank port ion interconnects with the firstouter shank portion at the first free shank end, and the second innershank portion interconnects with the second outer shank portion at thesecond free shank end, and wherein the center lines of the components ofthe first inner shank portion and the first outer shank portion, and aload line extending between the free shank ends under load, do not allintersect at a single common intersection point, and wherein the loadline intersects with the center line of said first outer shank portionat an intersection point located closer to a central portion of the toolholder, along the center line of said first outer shank portion, thanthe intersection point at which the center line of the first inner shankportion and the center line of the first outer shank portion intersect;whereby in the event of a load urging the free shank ends apart, amoment is introduced by the load, forcing the connection surfaces of thefree shank ends apart only essentially along the extension of the loadline, thereby preserving the first angular orientation.
 14. The toolholder of claim 13 further characterized in that: the first bracket hasa defined center line, wherein the center lines of the first bracket,the first outer shank portion, and the third outer shank portion definea moment arm between: the center line of the first outer shank portionof the outer C-shaped frame; and an intersection of the center line ofthe first bracket and the center line of the third outer shank portionof the outer C-shaped frame.
 15. The tool holder of claim 13, whereinthe construction portion of the inner C-shaped frame and and twobrackets of the plurality of brackets connecting the constructionportion of the inner C-shaped frame to the outer C-shaped frame arefabricated as a unitary triangular frame element.
 16. The tool holder ofclaim 15, wherein the unitary triangular frame element has an attachmentpoint for carrying the tool holder.